Channel selection



April 25. 1933. H. A. AFFEL CHANNEL SELECTION Filed NOV. 14, 1931 3Sheets-'Sheet l MQSE QST SS INVENTOR vATTORNEY April 25, 1933. H A AFFEL1,905,359

CHANNEL SELECTION Filed Nov.'14, 1951 s sheets-sheet 2 AIZ: Rec.Distributor ATTORNEY April 25, 1933.

H. A. AFFEL CHANNEL SELECTION Filed NOV. 14V, 1931 3 Sheets-Sheet 3INVENTOR ATTORNEY rammed, Api. 25, A1933 uNiTlzo STATES PATENT ori-icaERIAN A. AEREI, 0F RIDGEWOOD, NEW JERSEY, ASSIGNR T0 AIlBICAN TELE-PHONE AND TELMBAPH COMPANY, A CORPORATION F NEW YORK,

om america limitation mea rovente; 14, isai. sei-iai no. 575,124.

distance telephone circuits, carrier telephone circuits, two-way radiocommunication circuits, etc. In fourf: ao

wire'cable operation, for example, a pair of wires together with thenecessary terminal ap ar'atus and intermediate repeaters are de nitelyassigned for transmission in each direction. Similarly, in the case ofcarrier communication a frequency band with the required terminalapparatus and intermediate amplification is set aside for each directionof transmission. Qonsiderin the idle periods due'to time lost in switcing and making connections, incidental pauses in conversation, etc., along distance circuit is at best actually carrying speech only a part ofthe time. In the case of a two-way communication circuit of thefour-wire type where a'separate transmission path is set up in eachdirection, this ineliiciency in the use of the communication channel isaggravated by the fact that when one channel is. being used fortransmission in a given direction, the channelv in theopposite directionis usuallv idle. In'other words, even after the communica- -tion'is setup and the subscribers have control of the circuit, each one-way path ofa four-wire circuit is used at an average efficiency of only percentbecause on the avera e, transmission `takes place in each direction onlyabout one-half of the time.

. This lack of efficient use of the circuit facilities may 'not be ofsuch serious consequence in connection with theaverage telephonecircuit. However, in connection with super-distance circuits such astransoceanic radio, or the proposed transatlantic telephone cable, thetalking paths provided are necessarily very expensive and anyimprovementin the eiliciency of use will be proin other forms of v the groups ofcircuits existing between the that theyv may be set up not as individualcircuitsv with definite cilities assigned for the period o aconversation but rather that the choice ofa particu-l lar idle circuitmay be made automatically each time the subscriber s ks. Thisarrangement lends itself particularly to operation in the case offour-wire circuits where the one-way trunks can be grou ed to ther ineach direction. In the case of a s ciently large number of circuitsbetween two points the proposed method of operation offers thepossibility of providing for at least twice the number of simultaneousconversations-obtained with existing arrangements in which the twoseparate directional paths are definitely set up to form a particulartwoway circuit.

The arrangement for selecting channels automatically each time thesubscriber speaks may obviously assume many forms, and for purposes ofillustration only, a commutator type of selecting arrangement is hereinillustrated. Upon this commutator Aarrangement all of the one-way trunksterminate, and rotating switch arms are connected to the subscribersterminals, these switch arms being capable of speedily covering in asingle-revolution all of the switch points representing the terminationsof the grou spea s his voice operates relay arrangements to cause therotating arm at his terminal to pause in its rotation at an idletrunk.The

physical faof trunks. When the subscriber rotating switch arms at thetwo subscribers terminals are arranged to rotate synchronously so thatthe corresponding switch arm at the receiving end will also be causedtopause at the desired points by virtue of the voice potentials appearingat the receiving terminal. v While the foregoing arrange; ment serves toillustrate the principles involved, it will be understood that theinvention is not confined to any particular type of selectingarrangement.

The mvention will now be more fully understood when read in connectionwith the accompanying drawings, in which Figure 1 is a schematic layoutshowing in a general way the manner in which the trunks are associatedwith the terminal stations which they serve to connect; Fig. 2 is acircuit arrangement showing the manner in which the trunks areassociated with the transmitting selecting apparatus at one terminal;Fig. 3 similarly shows how the trunks are associated with the receivingselecting apparatus at the other terminal; and Fig. 4 is a detailshowing the coupling between the distributor arm and the driving shaftfor the various distributors.

As previously stated, no regular circuit assignments of the one-waychannels between two points will be made, but in connection with thesubscribers talk, each time a person speaks he will automatically pickout an idle trunk-not a .particular circuit, but merely one which atthat time is not in use. The general la out of such a scheme is shown inFig. 1. ere two sets of terminals are shown connected by a number ofone-way trunks. In the exam le illustrated the trunks are eight in numer in each direction and are desi ated A, B, C, etc., from west toeastand A, BB, CC, etc., from east to west. These trunks may be one-waycable circuits for trans'ooeanic telephony, radio channels, or telephonetransmission circuits of any type. If the practice of the prior art werefollowed, one set of trunks would be used for transmission in eachdirection, that is, two channels, one for each direction, would provideone talking circuit and the total number illustrated would, therefore,provide eight four-wire tratlic circuits. The proposed arrangement,however, permits approximately double this number of talking circuits.

Each talking circuit is provided with a speech controlled distributorarrangement comprising two distributors at each end of the circuit, asshown schematically on the drawings. Four sets of distributors are shownout of a possible number approaching sixteen, the sending distributorsat the West terminal being designated TD1, TD2, etc., the receivingdistributors at said terminal being designated RD1, RD2, etc., while thecorresponding distributors at the east terminal have similar referencecharacters primed. One transmitting distributor and one receivingdistributor are associated with each line terminal. When a person talks,for example, at the No. 1 terminal west, the

- transmitted speech will reach the associated sending distributor TD1.The function of this distributor is to pick out approximatelyinstantaneously one of the idle sending trunks designated A to H,inclusive. For the duration of the articular word or phrase spoken bythe ta er the connection will be established over this particular trunk.At the receiving terminal the trunk will be correspondingly switchedmeans of the reb ceiving distributor RDl'y to the No. 1 terminal for thesame period of time. As soon as the talker finishes the word or phrasethe trunk will be released and will then be available for any othersubscriber talking in that direction. The arrangement of course,functions simultaneously in t e reverse direction. Thenature of and theconnections to the sending and receiving distributors are shown in Fi 2and 3, respectively. In Fig. 2 only t e sending distributors associatedwith the terminals are shown, and in Fig. 3 only the receivingdistributors associated with the corresponding terminals at the otherend are shown so that the actual circuit arrangements illustrated onlytake care of transmission in one direction, the similar arrangements fortransmission in the op osite direction being schematically indicated).

Each distributor consists of a commutator having several sets ofsegments passed over by brushes attached to a rapidly rotating switcharm. Each set of segments corresponds to one of the one-way trunks towhich the distributor has access. In the case illustrated the number oftrunks is four and, consequently, the number of sets of segments islimited to four, but with an increase in the numberof trunks the numberof sets of segments will obviously be correspondingly increased. Also itwill be noted that while only three sendingdistributors are illustratedat the one terminal and three receiving distributors at the otherterminal, the number of distributors sending or receiving as the casemay be at each terminal will correspond to the number of terminalstations which may approach twice the number of trunks transmitting in agiven direction. For example, if there are four west to east trunks,there might be upwards of eight terminal stations at each terminal, andhence, upwards of eight transmitting distributors and a similar numberof receiving distributors at each terminal. If the number of west toeast trunks is increased to, say, twenty, the number of terminalstations at each terminal will then approach forty witha correspondingincrease in the number of distributors.

Each distributor is provided with a rotating brush arm such as BA1 towhich are attached brushes which pass over the various segments. Therotation of this brush arm is governed by a shaft common to all of thedistributors at a particular terminal and the connection between therotating arm and shaft is of the frictional type permitting the arm tobe held by a stop clutch mechanism arranged to stop the arm at any setof commutator segments while the shaft continues to revolve. 1

5 For reasons which willaappear more fully hereinafter it is desirablethat when a particular' arm is stopped and then again released, itshould start in rotation again in the same phase relation with respectto other rotating distributor arms on the same' shaft that existedbefore the arm was stopped. To permit of this possibility the frictionclutch arrangement etween the brush arm and the shaft ma be of the typeillustrated in Fig. 4 where t e brush arm BA is freely mounted upon-therotating shaft 20. The rotating shaft 20 is provided with a shallowsocket into which may enter a ball 21 carried in a suitable recess inthe brush arm and spring pressed a ainst the shaft by a spring 22.Whenever t e brush arm BA is held by the'stop clutch arrangement, theball 21 will ride out of the socket in the shaft 20 and the shaft willcontinue rotating while the brush arm is held stationary. When the brusharm is again released the friction between the ball 21 and the shaft 20is not suiicient to set the brush arm again into motion until the shaftrotates to the point where the ball 21 can again ride into the socketprovided for it, whereupon the brush army will again rotate in the samephase relation which had previously existed with respect to otherrotating brush arms on the same shaft.- Presumably the brush arms forthe diiferent distributors should each occupy a different normal angularposition with res ect to the shaft, and consequently, the soc ets forthe balls such as 21 on the vari- 4) angular positions as shown indotted lines in Fig. 4. For example, in the case illustrated in Fig. 2,-where there are four trunks and may be as many aseight sendingdistributors and, consequently, eight sending brush arms associated withsaid trunks, there should be eight different angular positions for thebrush arms and hence, the several sockets corresponding to the brusharms- TD1 and the receiving branch leads to the'- correspondingreceiving distributor, not shown. The connection to the receiving disousbrush arms will be arranged in diiferent should be 45 degrees apart. Theangularv tributor will be as indicated from the correi sponding hybridcoil HC1 at the opposite terminal (see Fig. 3). The transmittingc0nnection from the hybrid coil is in turn divided into two branches oneof which includes an amplifier-detector such as shown at AD1, the

function of this amplifier-detector bein to produce an operating currentfor control ing the switching operations to be later described. Theother branch includes a delay circuit for holding u the transmission ofthe speech currents until the switching operation has taken place. 1

Each set of commutator se ents comprises four segments of which t eouter air is connected to a trunk such as the trun D and of which theinner pair is connected to a relay such as the relay R11 of Fig. 2. Thebrush arm carries a correspondin number of wi ers. Each distributor, as,or example, t e distributor TD1, is provided with four sets of stopmagnets, one for each set of commutator segments, the stop magnets beingdesignated SM1., SM1, etc. One of these stop magnets corresponds to eachof the trunks A, B, etc., and Awhen the trunk is idle the stop magnet-will be deenergized so that a detent upon its armature will be in thepath of a corresponding detent upon the armature of a voice-operatedrelay VR1 carried by the brush arm. Consequently, if the voice-op-lerated relay VR1 is energized, its armature will engage with the detentof the first stop magnet which it encounters and brings the brush arm torest upon the corresponding set of commutator segments. The relays, suchas R11, R11, etc., associated with the several sets of commutatorsegments of a given distributor, serve the purpose of energizingcorresponding stop ma ets of other distributors, thereby with rawingtheir armatures and rendering the corresponding segments of such othercommutators busy so that the brush arms of such other commutatore willnot stop at a corres nding position. The voice-operated relay' 1 isconnected to the output of the amplifier-detector AD1 and loo thereforeonly swings the detent of its armature into the path of the detent of anonenergized stop magnet when voice waves arrive from the terminal 1.Each brush arm also carries a wei hted switch arm such as S1. Theinertia o the switch arm serves to hold open a contact in the talkingcircuit from the delay network DN1 while the brush arm is in rotation.When the brush arm comes to a stop, however, the momentum of the switcharm causes it to close said contact. This prevents talking currentsbeing picked up from talking segments over which the brush arm therebycausing vthe possibility of false operation, as will be explained later.

The above general description applies to all of the sending distributorarrangements ias asses during its rotation and iso shown in Fig. 2. Theapparatus associated with the several receiving distributors shown 5corresponding reference characters prime The essential diiferencebetweenthe sending and receiving distributors is that the amplifier-detectorarrangement such as AD1 of Fig. 3 is connected to the outer brushes'ofthe brush arm, and therefore serves to rectify currents incoming fromone of the trunks such as D to the corresponding talking segments of thedistributor. The output of the amplifier detector is then connectedthrough one branch to the voice-operated relays such as VR1 which servesto stop the brush arm, and through `another branch to the brushes whichpass over the control segments such as CS 1d to which the relayssuch asR 1d are connected: The talking brushes of the brush arm are connectedover a branch ahead of the amplifier-detector to the receiving side ofthe hybrid coil such as HC1. This talking connection is normally heldopen during rotation by a weighted switch arm such as S 1 similar to theswitch arm described in connection with the sending distributor.

Further details of the apparatus will be clear from a description of theoperation,

`which is as follows:

Let us assume that a subscribers line is connected to the jack` 1 andthat the subscriber is carrying on a conversation with-anothersubscriber whose line is connected to the jack 1. If the subscriberconnected to the jack 1 should speak, voice currents would pass into thetransmitting connection from the hybrid coil and enter the delay networkDN1 which serves to delaly7 the transmission of the voice currents untilt e voice-operated relay VR1 has operated. Some of the voice energy willbe diverted into the amplifier-detector AD1 and appear upon the outputside thereof in rectified form. A part of the rectified current thenenters the .Winding of the voice-operated relay VR1 to energize saidrelay and thereby cause the detent on the armature of the relay to bemoved into such a position that it will engage the corresponding detentof any deenergized stop magnet. All stop magnets correspond to any ofthe trunks A, B, C, D, which are at the moment engaged will be energizedand have the detents of thelr armatures drawn out of the detent of thearmature of the voice relay VR1.

If we assume that the trunk D is at the moment not engaged, the stopmagnet SM111 will be deenergized at the moment the wipers of the brusharm BA1, pass over thel group of segments opposite the stop magnet SMM.Consequently, the detent on the armature of the voice relay VR1 engagesthe detent on the stop magnet SM'111 and therefore brings the brush armto rest with brushes upon the corresponding group of segments.

When the brush arm thus comes to rest, some of the rectified current onthe output side of the amplifier-detector AD1 asses over the inner airof brushes of the rush arm and over t e segments CS111'tothe winding ofthe relay R11. Relay R11 is thereby energized and connects ground to thewire d. All of the stop magnets of the various distributors whosesubscripts are d are connected to the now grounded wire d and hence, allof the stop magnets such as SMM and SMM of other distributors will beenergized and their armatures will be pulled out of the paths of txthedetents of the voice rela s carried by other rotating brush arms.onsequently, any other brush arms that are rotated will not be stoppedon the segments corres ondin to the trunk D. The stop magnet @M11 ofgthe distributor associated with terminal 1, however, is not energized bythe connection of ground to the Wire d as the engagement of its detentwith the detent of the voice relay VR1 connects a short circuit aboutits wind- 1ng.

4 During the time that the brush arm was rotating, a weighted switch armS1 carried by the brush arm was by its inertia caused to rest upon aninsulated back contact carried by the brush arm BA1. When the brush armcame to rest, however, in the manner above described, the momentum ofthe Weighted switch S1 caused it to move forward against its frontcontact, thereb completing a circuit from the output sidse of the delaynetwork DN1 to the outer brushes of the brush arm and over the speechsegments SSM to the trunk D. During the time necessary for the brush armto rotate until it comes to rest upon the segments corres onding to anidle trunk, the voice currents rom the terminal 1 are prevented frombeing transmitted by the open switch S1. After the brusharm has come torest and the weighted switch S1 has completed the talking circuit, thevoice currents pass through the delay circuit and over the sech-segments SS11 to the trunk D.

W ile the brush arm BA1 was rotating with its voice relay VR1 energized,it did not come to rest upon the segments corresponding to an vtrunkwhich at the moment was engage because all such trunks had their stopmagnets energized so that the detents were drawn out of the path of thedetent of the voice relay VR1. For example, if we consider the trunk Cand refer to the distributor TDS which is shown resting upon thesegments corresponding to the stop magnet SMBC, it will be seen that therelay R3., is energized to put groundupon the wire c which energizes thestop magnet SM1c of the distributor TD1. Therefore, the brush arm BA1could not have come to rest upon the segments corresponding to the trunkC. Furthermore, as will be explained later, there is no possibility thattwo brush arms of dif- :ferent distributors whose voice relays are atthe same moment energized by talking currents will come to rest uponsets of segments corresponding to the same trunk because the brush armswhen rotated will always be out of hase with each other.

e have now traced the operation to the point where the'terminal 1 hasbeen connected to the trunk D and the voice. currents are passing overthe trunk D. We will now see how the correspondin terminal 1 isconnected tothe same t D and no other during the continuance of the rainof voice waves from the terminal 1. he voice currents now transmitted tothe trunk D ass over said trunk'to the s eech segments S'm of thereceiving distri utor RD1 and also pass to the corresponding speechsegments of the distributors of the' other receiving ter- 2) minals. Thebrush arm BA1 during its continuous rotation has its receivingconnection from its outer segments to the hybrid coil HC1 held open bythe inertia of the weighted switch S1 so that any speech currents picked2 upfrom talking trunks as its outer brushes pass over the speechsegments corresponding to such trunks are not transmitted to theterminal 1 so long as the brush arm continues to rotate. Each timethe'outer brushes pass `over energized speech segments, voice currentspass to the amplifier-detector AD1 and some of the rectified outputenergy causes voicerelay VR1 to move its detent outward` ly. `The brusharm is not brought to rest, -5- however, upon a set of segments whosespeech segments are ener ized, if the corresponding trunk has alreadyeen switched into connection with another talking terminal such as theterminal 3', because in that case the cor- 73 responding stop magnet ofthe distributor RD'1 will be energized under the control of' some otherdistributor in a manner which will be described later. Furthermore, thebrush arm of the distributor RD1 will not be brought to rest upon agroup of segments that are not energized by speech currents, because inthat case the relay VR1 will no't be energized as the brush arm passesover such set y of segments, and hence its detent cannot enf gage thedetent of the stop magnet.

In other words, the brush arm will not come to rest upon the set ofsegments corresponding to an idle trunk. It can only come to rest uponsegments corresponding to a trunk which at the moment is applying speechcurrents to the speech segments of the set of segments. And it cannotcome to rest upon a set of segments corresponding to a trunk which hasalready been connected to some other terminal. It will come to rest,however, upon the set of segments corresponding to the trunk D becausethat trunk will not have been connected by any other distributor to anyother terminal than the C5 terminal 1 and hence, its stop magnet SMmwill be amel-gized a the moment the brush.

arm gasses over the group of segments correspon ing to the trunk- D. Aswill be more fully explained hereinafter, -all ofthe receiving brusharms which are in rotation have: fixed angular positions with respect tothe rotatin shaft which are out of hase with each ot er so that only onebrus armwill pass over a Set of energized segments at a time.Furthermore, 'the synchronism' between the rotating shafts at thetransmitting end and at the receiving end is such that when the brusharm BA1 at the sending end comes to rest and transmits voice currentsover the trunk D, the voice currents will arrive at the receiving end ofthe trunk D and will be applied to the corresponding speech segmentsSSH., just before or at the moment the outer brushes of the receivingbrush arm BA1 are passing over said speech segments. Consequently, thevoice relay VR1 is ener ed and its detent engages the detent of momentis energized. This brings the' brush arm BA1 to rest on the set ofsegments corresgmnding to the trunk D.

ome o the rectified voice energy now aps..

pearing on the output side of the amplifierdetector ADQ passes to theinner or control se ments CSm and thence to the relay R 1d. This relayis therefore energized and applies ground to the wire that all of thecorresponding stop magnets of other receiving distributors are ener'zed. Stop magnet SMm of the distributor R 1 is not energized, however,as its winding is short-circuited by thecontact between the detent ofits armature with the detent of the; voice relay V'Rl. The switch armnow remains at rest on the set of segments corresponding to the trunk Dand will remain asso-I If during the time that speech is incoming A fromtrunk D and the brush arm BA1 is resting upon the segments of thedistributor RD1 corresponding to said trunk, the brush' arm of any otherreceiving distributor passes over the contacts of such other distributorwhich corresponds to the trunk D, the brush arm of such otherdistributor will not come to rest even though its voice relay isenergized.

For example, suppose the brush arm BA2 rotates over the segmentscorresponding to the 1 trunk D with the result that its voice operatedrelay V12/2 is energized at that moment. It

e corre' spondmg stop magnet SMM which at thev izo cannot come to restbecause the ound applied to the wire d b the relay 1d of the distributorRD1 will ave energized the stop ma et SMZ., to pull its detent out ofthe pat of the detent of the voice relay VR2.

It will, of course, be obvious that any brush arm of any distributorwill be released as soon as voice currents cease to energize its voicerelay. For example, the transmitting distributor TD1 will have its brusharm released as soon as voice currents cease to arrive from the terminal1 because the voice relay VH1 will be deenergized and its detentwithdrawn from contact with the detent of the stop magnet SMM.Similarly, the receiving brush arm BA'1 will be released and start intorotation a ain as soon as voice currents cease to arrive rom the trunkD, for the voice relay VR1 will be deenergized and as a consequence itsdetent will be withdrawn from contact with the detent of the stop magnetSMM. As soon as the two brush arms commence to rotate the previouslyenergized relays, Rm of the transmitting distributor and R 1d of thereceiving distributor, will release and remove ground from the wires dand d', respectively, to release the corresponding stop ma ets of otherdistributors.

If or inary friction drive arrangements were employed between driveshafts and the brush arms it would be possible for the brush arms of twosending distributors to rotate in phase with each other and in responseto voice currents arriving from two sending terminals at the sameinstant come to rest with their brushes on the segments corresponding tothe same trunk. There would then be a possibility that the two brusheson the corresponding air of receiving distributors (which would)presumably be rotating in phase) would come to rest and connect tworeceiving terminals to the same trunk. This not only would cause a crossconnection but might resultin getting the brush arms of correspondingsending and receivin distributors out of proper synchronism with respectY to each other if no arran ment were provided to prevent this actlon. Areceiving distributor would get out of properV synchronous relation toits corresponding transmitting distributor if, under the conditionsabove mentioned, one of the transmitting distributors was released bythe cessation of voice currents from its terminals before the othersending distributor is released. The two receiving distributors whichwere stopped upon the same trunk would inevitably be released at thesame time upon the cessation of talking current from the trunk to whichthey are connected. The sending distributors would, however, only beheld upon the trunk Vso long as talk was incoming from the sendingterminals with which the distributors vare associated. Consequently,when all four of the distributors synchronous relation to thecorrespondm receiving brush arm at the opposite termmal.

The diiculties referred to in the previous paragraph are overcome inaccordance with the arrangement disclosed by providing means to assurethat when a set of brush arms of distributors at a given terminal arerotated they will always rotate in a fixed angular relationship with rest to the rotating shaft and will be out o hase with each other. This maybe accomp ished by means of the arrangement previously described inconnection with Fig. 4. In this figure let 20 represent the rotatingshaft with which all of the brush arms of the various distributors at agiven switching station are associated. Each brush arm is connected tothe shaft by means of a ball pressed by a spring 22 which ball rests ina socket in the shaft 20. When the ball is in the socket the frictionalengagement between the brush arm BA and the shaft 2() is suilicient tocause the brush arm to rotate. When the brush arm is held by engagementwith a detent, as previously described, the ball 21 will ride out of thesocket and the shaft will continue to rotate without carrying the brusharm with it.v The sockets in the shaft 20 for the various brush arms ofthe various distributors will be arranged at different angular positionsabout the shaft 20 as indicated in dotted lines in Fig. 4 to show theangular position of a second brush arm. Consequently, when any brush armis released it will remain stationary until the shaft has rotated tobring its own socket into proper relationship, whereupon the ball entersthe socket and the brush arm then rotates with the shaft in the sameangular position with respect to the shaft which it occupied before itwas stopped by engagement with the detent.

Each brush arm, therefore, when rotated must necessarily rotate in adilferent phase relation with respect to every other brush arm.Consequently, if two subscribers at the sending terminal should bothcommence talking at the same time, there is no possibility of twosending brush arms stopping upon the segments corresponding to the samesubscriber. For example, if the subscribers corresponding to terminals 1and 2 should both commence talking at once and the brush arm of.distributor TDl is ahead of the brush arm of distributor TD2, theterminal 1 will be connected to the first idle trunk and will lock outthe distributor associated with terminal 2 from connection to that idletrunk. The distributor associated with terminal 2 will then select thenext idle trunk. If by a similar relationship of distributor arms todriving shaft the receiving distributors of Fig: 3 are rotating out ofphase with each other but in pro r synchronous relationship to thecorrespon ing sending distributors, voice currents will arrive at thereceiving end over the trunk connected to the terminal 1 before theywill arrive over the trunk connected at the terminal 2, because theconnection to terminal 1 was completed before the connection to terminal2. Since the brush arms of the corresponding receiving` distributors areeach in proper synchronous relationship to its corresponding sendingdistributor, the brush arm of the distributor associated with terminal 1will come to rest upon the trunk to which the terminal 1 is connected byvirtue of the fact that it will be passing over the energized speechsegments of such trunk at the moment voice currents arrive over suchtrunk. Similarly, the brush arms of the distributor associated with theterminal 2 will come to rest upon the segments associated with the trunkwhich was connected to vthe terminal 2 because the voice currents willarrive from its trunk after the voice currents have arrived from theterminal 1 and will arrive at the moment the brush arm associatedwithterminal 2 passes over the corresponding segments. This takes placenotwithstanding that speech started from terminals 1 and 2 at the sameinstant. The delay in the arrival of speech at the terminal 2 is due tothe fact that an idle trunk was conneced to the terminal 2 after theidle trunk was conA nected' to the terminal 1. v

`By means of the mechanical connection between driving shaft and brusharms above described and with the sockets in the shaft correspondin todifferent brush arms all arranged in di erent angular positions, it willbe evident that when any brush arm is stopped and then again released,it will always start rotating in the same angular position wi'h respectto its shaft that it occupied before it was stopped. Hence if the shaftof a set of sending distributors is in synchronism with a shaft ofreceiving distributors, each sending brush arm will rotate in propersynchronous relation to each receiving brush arm no matter when it isstopped nor how long after it is stopped it is again released. Thus thepossibility of false switching connection being made between twoterminals is avoided.

It will be obvious that the general principles herein disclosedv may beembodied in many other organizations widely different from thoseillustrated without departing from the spirit of the invention asdefined in the following claims.

What is claimed is:

1. In a signaling system, a pair of switching stations, trunks extendingbetween said stations, a signaling terminal at one station, and meansresponsive to sound currents incoming from said terminal to select andconnect thereto an idle trunk.

2. In a signalin system a pair of switching stations, trunEs exten ingbetween said stations, a signalin terminal at one station, and meansresponsive to sound currents incoming from said terminal to select anidle i trunk and maintain said trunk connected to said terminal onlyduring the continuance of sound currents.

3. In a signalin system, a pair of switching stations, trun s extendingbetween said stations, a signaling terminal at one station, and meansresponsive to sound currents incoming from said terminal to select andconnect thereto an idle trunk, and means to release said trunk upon thecessation of sound currents.

4. In a signalin system, a pair of switching stations, trun s extendingbetween said stations, a signaling terminal at one station, and meansresponsive to sound currents incomin from said terminal to select andconnect t ereto an idle trunk, means to release said trunk upon thecessation of sound currents, and means to select and connect to theterminal a new trunk upon the initiation of a newA train of soundcurrents.

5. In a signalin system a pair of switching stations, trun s extendingbetween said stations, signaling terminals at each station arranged tointercommunicate in pairs between stations, and means responsive tosound currents incoming from one terminal to select and connect theretoan idle trunk, and means to connect said trunk to the correspondingterminal at the other station.

6. In a signaling system, av pair of switching stations, trunksextending between said stations, signaling terminals at each stationarranged to intercommunicate in pairs between stations, and meansresponsive to sound currents incoming from one terminal to select andconnect thereto an idle ti'lmk, and means to connect said trunk to thecorresponding terminal at the other station, said trunk remainingconnected only during the continuance of said sound currents.

7. In a signalin system, a pair of switching stations, tr s extendingbetween said stations, signaling terminals at each station arranged tointercommunicate in pairs be.

tween stations, means responsive to sound currents incoming from oneterminal to select and connect thereto an idle trunk, and means toconnect said trunk to the corresponding terminal at the other station,and means to release said trunk upon the cessation of said soundcurrents.

8. In a signaling system, a pair of switching stations, trunks extendingbetween said stations, signaling terminals at each station arranged tointercommunicate in pairs between stations, means responsive to soundcurrents incoming from one terminal to select and connect thereto anidle trunk, and means to connect said trunk to the correspondingterminal at the other station, means to release said trunk u on thecessation of said sound currents, an means to select and connect to thesame terminals a new trunk upon the initiation of a new set of soundwaves.

9. In a signaling system, a vpair of switching stations, a group oftrunks extending between said stations for transmission in onedirection, a. second group of trunks extending between said stations fortransmission in the opposite direction, signaling terminals at eachstation arranged to intercommunicate in pairs betwen stations, meansresponsive to sound currents incoming from one signaling terminal toselect an idle trunk from one group and connect it to said terminal,means to connect said trunk to the corresponding terminal at the otherstation, means responsive to sound currents incoming from said lastmentioned terminal to select a trunk from the other group and connect itto one terminal, and means to connect it to the other terminal.

10. In a signaling system, la pair of switching stations, a group oftrunks extending between said stations for transmission in onedirection, a second group of trunks extending between said stations fortransmission in the opposite direction, signaling terminals at eachstation arranged to intercommunicate in pairs between stations, meansresponsive to sound currents incoming from one signaling terminal toselect an idle trunk from one group and connect it to said terminal,means to connect the selected trunk to the corresponding terminal at theother station, means responsive to sound currents incoming from saidlast mentioned terminal to select a trunk from theother group andconnect it to one terminal, and means to connect it to the otherterminal, said trunks remaining connected only during the continuance ofsaid sound currents. l

11. In a. signaling system, a pair of switching stations, a group oftrunks extending between said stations for transmission in onedirection, a second group of trunks extending between said stations fortransmission in the opposite direction, signaling terminals at eachstation arranged to intercommunicate in pairs between stations, meansresponsive to sound currents incoming from one signaling terminal toselect an idle trunk from one group and connect it to said terminal,means to connect the selected trunk to the corresponding terminal at theother station, means responsive to sound currents incoming from saidlast mentioned terminal to select a trunk from the other group andvconnect it to a terminal, means 66 to connect it to the other terminal,and

ing from one signaling Vterminal to select' an idle trunk from one groupand connect it to said terminal, means to connect the selected trunk tothe corresponding terminal at the other station, means to release saidtrunk upon the cessation of sound currents from said terminal, means toautomatically reselect a trunk from said group upon the initiation of a.new set of sound waves from the same terminal, means responsive to soundcurrents incoming from said terminal at the other station to select atrunk from the other group and connect it to' a terminal, and means toconnect it to the other terminal, means to release said trunk upon thecessation of sound currents from said last mentioned terminal, and meansto automatically reselect a trunk from said second group upon initiationof a new set of sound currents incoming from said last mentionedterminal.

13. In a signaling system, a pair of switchin stations, a plurality oftrunks extending tween said stations, signaling terminals connected toeach station and arranged to intercommunicate in pairs between stations,each terminal terminating at its switching station in a transmittingbranch and a receiving branch, means responsive to signals from oneterminal in its transmitting branch to select and connect thereto anidle trunk, and means to thereupon connect said trunk to the receivingbranch of the corresponding terminal at the other ation.

'14. n a signaling system, a pair`of switching stations, a plurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to intercommunicate in pairs between stations,each terminal terminating at its switching station in a transmittingbranch and a receiving branch', means responsive to signals from oneterminal in its transmitting branch to select and connect thereto anidle trunk, and means to thereupon connect said trunk to the receivingbranch of the correspondingterminal at the other station, said trunkremainin connected only during the continuance of said signals.

15. In a signaling system, apair of switching stations, a plurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to inliw tercommunicate in pairs betweenstations, each terminal terminating at its switching station in atransmitting branch and a receiving branch, means responsive to signalsfrom 5 one terminal in its transmitting branch to select and connectthereto an idle trunk, means to thereupon connect said trunk to thereceiving branch of the corresponding terminal at the other station, andmeans to release said 10 trunk upon the cessation of said signals.

16. In a signaling system, a pair of switching stations, a plurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to intercommunicate ,in pairs betweenstations, each terminal terminating at its switching station in atransmitting branch and a receiving branch, means responsive to signalsfrom one terminal in its transmitting branch to 20 select and connectthereto an idle trunk,

means to thereupon connect said trunk to the receiving branch of thecorresponding terminal at the other station, means to release said trunkupon the cessation of said signals, and means to select and connect anew trunk to said transmitting and receiv: ing branches upon theinitiation of a new set of signals to be transmitted in the same d1-rection.

3 17. In a signaling system, a pair of switching stations, a pluralltyof trunks extending between said stations, signaling terminals connectedto each station and arranged to intercommunicate in pairs betweenstations, each terminal terminating at its switching station in atransmitting branch and a receiving branch, means responsive to signalsfrom one terminal in its transmitting branch to select and connectthereto an idle trunk, means to thereupon connect said trunk to thereceiving branch of the corresponding terminal at the other station, andmeans to select and connect another trunk between the transmittingbranch of said second terminal and the receiving branch of said firstterminal upon the initiation of a set of signals at said secondterminal. l

18. In a signaling system, a pair of switching stations, a plurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to intercommunicate in pairs between stations,each termina-l terminating at its switching station in a transmittingbranch and a receiving branch, means responsive to signals from oneterminal in its transmitting branch to select and connect thereto anidle trunk, means to thereupon connect said trunk to the receivingbranch of the corresponding terminal at the other station, and means toselect and connect another trunk between the transmitting branch of saidsecond terminal and the receiving branch of said first terminal upon theinitiation of a set of signals at said second terminal, said trunksremaining connected for transmission in a iven direction only during thecontinuance o signals.

19. In a signaling system, a pair of switching stations, a Yplurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to intercommunicate in pairs between stations,each terminal terminating at its switching station in a transmittingbranch and a receiving branch, means responsive to signals from oneterminal in its transmitting branch to select and connect thereto anidle trunk, means to thereupon connect said trunk to the receivingbranch of the corresponding terminal at the other station, means toselect and connect another trunk between the transmitting branch of saidsecond terminal and the receiving branch of said first terminal upon theinitiation of a set of signals at said second' terminal, and means torelease said trunks upon the cessation of signals in a given direction.

20. In a signaling system, a pair of switching stations, a plurality oftrunks extending between said stations, signaling terminals connected toeach station and arranged to intercommunicate in pairs` betweenstations, each terminal terminating at its switching station in atransmitting branch and a receiving branch, means responsive to signalsfrom one terminal in its transmitting branch to select and connectthereto an idle trunk, means to thereupon connectsaid trunk to thereceiving branch of the corresponding terminal at the other station,means to select and connect another trunk between the transmittingbranch of said second terminal and the receiving branch of said firstterminal upon the initiation of a set of signals at said secondterminal, means to release said trunks upon the cessation of signals ina given direction, and means to select and connect a new trunk fortransmission in a given direction inresponse to the initiation of a newset ofsignals in that direction.

21. In a system in which a plurality of trunks extend between twostations and signalin'g terminals are provided at each station forcommunication in pairs between stations, the method which consists inconnecting an idle trunk between a given pair of terminals only duringthe continuance of sound waves from one of said terminals.

22. In a system in which a plurality of trunks extend between twostations and signaling terminals are provided at each station forcommunication in pairs between stations, the method which consists inconnecting an idle trunk between a given pair of terminals only duringthe continuance of sound waves from one of said terminals anddisconnecting said trunk upon the cessation of sound waves.

23. In a system in which a plurality of les trunks extend between twostations and signalin terminals are provided at each station orcommunication in pairs between stations, the method which consists inconnectin an idle trunk between a given pair of terminals only duringthe contlnuance of sound waves from one of said terminals, disconnectingsaid trunk upon the cessation of sound waves, and selecting andconnecting between the terminals a new idle trunk upon the initiation ofa new set of sound waves.

24. In a system in which a plurality of trunks extend between twostations and signaling terminals are provided at each station forcommunication in pairs between stations, the method which consists inconnecting an idle trunk between a given pair of terminals only duringthe continuance of sound waves from one of said terminals, disconnectingsaid trunk upon the cessation of sound waves, and selecting andconnecting between the terminals a new idle trunk upon the initiation ofa new set of sound waves from the other intercommunicating terminal.

In testimony whereof, I have signed my name to this specification this13th day of November 1931.

HERMAN A. AFFEL.

